In a recent LinkedIn post, serial entrepreneur James Caan laid out the five things you should never say or do in an interview. He strongly advises against showing up without questions and asking about vacation time or salary. He also says you should never bash your current or previous employers, and — perhaps his most difficult instruction of all — he suggests you avoid the phrase “I don’t know.”

Why? It tells the interviewer that you’re not prepared and can’t think on your feet.

“Interviewers will be looking to stretch and challenge candidates during the course of the recruitment process," Caan explains. " The best way of dealing with the tough questions is to do your homework."

If you’ve done sufficient research, you should be prepared for almost anything that may be asked of you about the company, the job, or your resume. Yes, you may be faced with a tough, unexpected query. In this situation, don’t fret and say, “I don’t know” — and you definitely shouldn’t bluff your way through a response. Instead, use the opportunity to show the prospective employer how you perform under pressure, to demonstrate your thought process and character, and to communicate your skills and values.

“Move back into your comfort zone, relate the question back to something you do know, and take on board any new information you are given,” Caan says.

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